The field of the invention is failure diagnostics for an internal combustion engine provided with a turbocharger, and more particularly power trains provided with two staged turbochargers.
The air supercharging of an engine makes it possible to increase the performance levels of the engine by accepting, for the combustion of the fuel, a mass of air greater than in an atmospheric engine of equivalent cylinder size.
A supercharging device can comprise a turbocharger, comprising on the one hand a compressor which supplies the engine with air at a pressure greater than atmospheric pressure, and on the other hand, a turbine that is passed through by the exhaust gases from the engine.
The power supplied to the turbine by these exhaust gases is transmitted, via a shaft, to the compressor which compresses the air sucked from the outside environment to a pressure called supercharging pressure.
With the current trend to increase the specific performance of the engines, the supercharging pressure values demanded of the turbochargers are becoming increasingly higher. The turbochargers are subject to very high mechanical stresses, which affects their reliability. It is therefore important to accurately control their state of operation and to diagnose the occurrence of any mechanical failure so as, for example, to limit the engine performance levels and/or to alert the driver of the need for a repair.
Also, these mechanical failures are often preceded by a turbocharger supercharging pressure regulation fault which can cause the legal level of the polluting emissions from the engine to be exceeded. The OBD (On Board Diagnosis) standards concerning embedded diagnosis on board vehicles require the driver to be alerted to any such overshoot. It is therefore important to diagnose the failure or the malfunction of a turbocharger in order to meet these standards.
Currently, the diagnosis of internal or external leaks in the supercharging intake circuit is based on the comparison of the integral of the turbocharger regulation loop deviation to a detection threshold. In the case of a failing compressor bypass, the measured pressure is lowered to the expected pressure, which makes it possible to detect a failure. Furthermore, there is a dead band above which the integral is not computed, in order to take into account the accuracy of the supercharging regulation. Similarly, the computation is not performed when the setpoint varies too rapidly.
The current diagnostics work only when the supercharging regulation is activated. Furthermore, these performance levels are highly dependent on the behavior of the control of the supercharging and of the control of the EGR. In practice, the calibrations greatly impact the supercharging response mask. Also, since the strategy is based on a looping error, an internal or external leak in the supercharging intake circuit will not be detected at stabilized rotation speed because of the action of the integrator of the supercharging regulator.
There is a need for a method and a system for diagnosing leaks that makes it possible to reduce the significance of the calibration and also that makes it possible to diagnose the power train operating at stabilized rotation speed.
There is therefore a need for a device for diagnosing the internal or external leak in the supercharging intake circuit that is capable of detecting the risk of an increase in polluting emissions, and the risk of high-pressure turbocharger overspeed.
In practice, an internal leak in the compressor bypass can lead to a reduction of the supercharging pressure and of the air flow rate, resulting in an increase in polluting emissions.
With an internal leak in the compressor bypass, the supercharging regulation will naturally compensate for the leak by rotating the high-pressure turbocharger faster potentially up to the destruction thereof because of an excessively high rotation speed.
An external leak can lead to a reduction of the supercharging pressure that the supercharging regulation will compensate for by rotating the high-pressure turbocharger faster potentially up to the destruction thereof because of an excessively high rotation speed.